The objective of the research is the identification of the non-K-region diols that are formed in vivo from carcinogenic polycyclic hydrocarbons and that are further metabolized to vicinal diol-epoxides that react with cellular nucleic acids. The situation with regard to benzo(a)pyrene is now clear and there is considerable evidence pinpointing the 7,8-dihydrodiol and the related 7 beta, 8 alpha-dihydroxy-9 alpha, 10 alpha-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene as the important metabolites. With other hydrocarbons that give rise to metabolites that react with DNA, the particular diols and diol-epoxides involved have not been identified. Preliminary studies have been carried out with benz(a)anthracene and these need to be continued and extended to include other polycyclic hydrocarbons like 7-methylbenz(a)anthracene, 7, 12-dimethyl-benz(a)anthracene, 3-methylcholanthrene and dibenz(a,h)anthracene. The long term aim of the work is, of course, an understanding of the way in which the modification of nucleic acids by polycyclic hydrocarbon metabolites causes biological effects that include mutagenesis and carcinogenesis.